Near-ultraviolet Research Articles

Thermal stable cyan-emitting Ba9(Lu1.5Ga0.5)Si6O24:Ce3+ for high color-rendering white LEDs

Cyan-emitting phosphors are key color converters for achieving a high color-rendering index (CRI) in white light-emitting diodes (LEDs). However, cyan phosphors that have a suitable excitation wavelength and high thermal stability are still challenges. In this work, the Ba9Lu1.5Ga0.5Si6O24:Ce3+ (BLGSO:Ce3+) cyan phosphor is studied. The excitation band has a peak at 395 nm, which is close to the emission light from the near-ultraviolet (NUV) LEDs (395-405 nm). BLGSO:Ce3+ manifests an emissive peak at 488 nm and a full-width at half maximum (FWHM) of 125 nm. Its internal quantum efficiency (IQE) reaches 90.7% at room temperature. At 150°C, the cyan emission intensity decreases to 97.2% of the initial value at room temperature, indicating excellent thermal stability. Combining with CaAlSiN3:Eu2+ and the 395 nm chip, a white LED with a high CRI of 91.9 is achieved.

New-Fashioned Universal and Functional Host-Material from a Near-Ultraviolet Organic Emitter for High-Efficiency Organic Light-Emitting Diodes with Low Efficiency Roll-Offs.

In this work, a near-ultraviolet (NUV) emitter, 2MCz-CNMCz, with hot-exciton property is designed based on a "long-short axis" strategy, which exhibits good thermal stability, bipolar carrier transport ability, and high T1 energy level. Its nondoped NUV organic light-emitting diode (OLED) achieves a record maximum external quantum efficiency (ηext ) of 7.76%, with a peak at 404nm and CIE coordinates of (0.158, 0.039). The corresponding high exciton utilization efficiency (ηr ) in the electroluminescence process reveals its potential as a functional sensitizing host. As expected, the TBPe-based blue fluorescent OLED with 2MCz-CNMCz as the host material shows better efficiency and lower efficiency roll-off than that with traditional host material mCP. Meanwhile, the Ir complexes-based green/yellow/red phosphorescent OLEDs with 2MCz-CNMCz host are also fabricated, reaching high ηext values of 26.1%, 30.4%, and 20.4%, respectively, and displaying negligible efficiency roll-offs at 1000cdm-2 , which are among the best OLED performances based on the same emitters. To the authors' best knowledge, this is the first report on the design of high-quality universal and functional host material, and may bring new inspiration to the preparation of high-efficiency, low roll-off, full-color OLEDs.

Structural, morphological and optoelectronic aspects of YAlO3:Dy3+ doped nanocrystalline materials for NUV energized WLEDs

Cost-effective urea assisted solution combustion (SC) synthetic method was employed to prepare a series of doped YAlO3:xDy3+ (0.01–0.08 mol) phosphors. The resulting powdered samples were comprehensively examined through various structural as well as optical measurements. Rietveld refinement studies concluded that prepared nanomaterials structured into the orthorhombic system having Pbnm (62) space group. Energy dispersive spectral (EDS) analysis was executed to observe the relative proportions of constituent elements in all doped nanophosphors. Transmission electron microscopy (TEM) micrograph indicated the presence of agglomerated particles with the average size in the nano range. Photoluminescence excitation (PLE) spectra showed that the designated phosphors could be excited by near ultraviolet (NUV) energized lighting sources. The strongest emission centred at 576 nm, corresponding to electric dipole (4F9/2 → 6H13/2) transition of Dy(III) ion. Furthermore, characteristics photometric parameters viz. correlated color temperature (CCT), chromaticity coordinates (x and y), and color purity (%) were figure out with the aid of PL data, which strongly endorsed their usage in NUV energized WLEDs applications.

Near-ultraviolet emitters based on carbazole-imidazole for highly efficient solution-processed organic light-emitting diodes

Solution-processable near-ultraviolet (NUV) and deep-blue organic emitters are crucial for the development of organic light-emitting diodes (OLEDs) in large-area production. However, such wide band gap materials with high photoluminescence quantum yield (PLQY) and stable electroluminescence are sparse. Here, three NUV and deep-blue solution-processable emitters, carbazole-imidazole derivatives, BuCzI, BuCzI-CN and BuCzI-BCN, are synthesized by employing 3,6-di-tert-butyl-carbazole at N1 position of imidazole as electron donor to construct a twisted and rigid structure of donor-linker-acceptor. The combination of carbazole and imidazole fulfills saturated NUV and deep-blue emission in solution and film, accompanied with excellent solubility in non-chlorinated solvents. Furthermore, the bulky donor of 3,6-di-tert-butyl-carbazole not only enhances localized excited and keeps high PLQY in different solvents, but also suppresses emission red-shift which results from intramolecular charge transfer (ICT) to realize NUV emission. The solution-processed undoped OLEDs fabricated with BuCzI, BuCzI-CN and BuCzI-BCN as emitters achieve external quantum efficiency (EQE) up to 3.30 %, 2.20 % and 2.63 % with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.04), (0.15, 0.06) and (0.15, 0.09), respectively. All devices retain stable NUV and deep-blue emission at varied applying voltages. The results of this work have provided a novel design strategy for NUV solution-processable organic emitters with high efficiency and stability.

Near-ultraviolet to visible spectroscopy of the Themis and Polana-Eulalia complex families

Context. Spectrophotometry data of asteroids obtained in the 1980s showed that there are large variations in their near-ultraviolet (NUV) reflectance spectra. Reflectance spectra at NUV wavelengths are important because they help detect the presence of hydrated minerals and organics on the asteroid surfaces. However, the NUV wavelength region has not been fully investigated yet using spectroscopic data. Aims. The aim of our study is to obtain the near-ultraviolet to visible (NUV-VIS, 0.35–0.95 μm) reflectance spectra of primitive asteroids with a focus on members of the Themis and Polana-Eulalia complex families. This characterization allows us to discuss the origin of two recent sample return mission target asteroids, (162173) Ryugu and (101955) Bennu. Methods. We obtain low-resolution visible spectra of target asteroids down to 0.35 μm using the telescopes located at the Roque de los Muchachos Observatory (La Palma, Spain) and revisit spectroscopic data that have already been published. Using new spectroscopic and already published spectrophotometric and spectroscopic data, we study the characteristics of the NUV-VIS reflectance spectra of primitive asteroids, focusing on data of the Themis family and the Polana-Eulalia family complex. Finally, we compare the NUV characteristics of these families with (162173) Ryugu and (101955) Bennu. In this work, we also study systematic effects due to the use of the five commonly used stars in Landolt’s catalog as solar analogs to obtain the asteroid reflectance in the NUV wavelength range. We compare the spectra of five G-stars in Landolt’s catalog with the spectrum of the well-studied solar analog Hyades 64, also observed on the same nights. Results. We find that many widely used Landolt’s G-type stars are not solar analogs in the NUV wavelength spectral region and thus are not suitable for obtaining the reflectance spectra of asteroids. We also find that, even though the Themis family and the PolanaEulalia family complex show a similar blueness at visible wavelengths, the NUV absorption of the Themis family is much deeper than that of the Polana-Eulalia family complex. We did not find significant differences between the New Polana and Eulalia families in terms of the NUV-VIS slope. (162173) Ryugu’s and (101955) Bennu’s spectral characteristics in the NUV-VIS overlaps with those of the Polana-Eulalia family complex which implies that it is the most likely origin of these two near-Earth asteroids.

High-performance non-doped near ultraviolet OLEDs with the EQE ∼ 6 % and CIEy ∼ 0.03 from high-lying reverse intersystem crossing

Developing high-performance organic fluorophors with short-wavelength emission is both significant and challenging subject in the application of organic light-emitting diodes (OLEDs). In this work, we proposes a “coupling hardness with distortion” design concept to construct an efficient near ultraviolet (NUV) fluorophor mP2MPC with 1,4-dimethyl-2,5-diphenylbenzene as a rotatable bridge via the meta-positons linking rigid and bulky phenanthroimidazole and carbazole groups. As a result, the non-doped OLED with it as emitter not only exhibits an emission peak at 395 nm with the Commission Internationale de l’éclairage coordinates of (0.163, 0.028), but also realizes a high forward-viewing external quantum efficiency of 6.09 % due to the high-lying reverse intersystem crossing. The value still keeps as high as 5.56 % at 1000 cd m−2, showing a small efficiency roll-off. This is one of the highest efficiencies among the non-doped devices with the electroluminescence peak below 400 nm. Moreover, the green and red phosphorescent OLEDs with mP2MPC as host can also show excellent electroluminescence performance with the forward-viewing external quantum efficiencies over 21.5 %, illustrating that mP2MPC should be a prospective material for OLEDs.

The Aditya-L1 mission of ISRO

AbstractThe Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, viz. a coronagraph observing in visible and infrared, a full disk imager in Near Ultra-Violet (NUV), and two full-sun integrated spectrometers in soft X-ray and hard X-ray. In addition, there are three instruments for in-situ measurements, including a magnetometer, to study the magnetic field variations during energetic events. Aditya-L1 is truly a mission for multi-messenger solar astronomy from space that will provide comprehensive observations of the Sun across the electromagnetic spectrum and in-situ measurements in a broad range of energy, including magnetic field measurements at L1.

Eu3+-Activated Alkali Rare-Earth Double-Tungstate Nanoparticles for Near-Ultraviolet-Light-Triggered Indoor Illumination

Phosphors for near-ultraviolet (NUV)-triggered white light-emitting diodes (LEDs) have become an attractive research topic in recent years. However, it is still difficult for phosphors to have simultaneous high luminous intensity, superior color purity, and excellent thermal stability. Hence, a series of Eu3+-activated alkali rare-earth double-tungstate nanoparticles with high luminescence intensity were prepared by a facile hydrothermal reaction method. The influence of rare-earth ions and alkali cations on the luminescence properties was investigated. Impressively, the prepared phosphors exhibit superior color purity and excellent thermal stability. Meanwhile, the emission intensity and color purity can be controlled by tuning the concentrations of Eu3+ ions. By employing the resultant nanoparticles, a fabricated LED device emitted bright warm white light with a high color rendering index (CRI) of 92.12 and a suitable correlated color temperature (CCT) of 4689 K. This work straightly confirms that the prepared phosphors are promising candidates as red-emitting components applied in NUV-triggered indoor illumination.

A Massive, Dusty, Hi Absorption–Selected Galaxy at z ≈ 2.46 Identified in a CO Emission Survey

We report a NOrthern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter/submillimeter Array search for redshifted CO emission from the galaxies associated with seven high-metallicity ([M/H] ≥ −1.03) damped Lyα absorbers (DLAs) at z ≈ 1.64–2.51. Our observations yielded one new detection of CO(3–2) emission from a galaxy at z = 2.4604 using NOEMA, associated with the z = 2.4628 DLA toward QSO B0201+365. Including previous searches, our search results in detection rates of CO emission of % and %, respectively, in the fields of DLAs with [M/H] > −0.3 and [M/H] < −0.3. Further, the Hi–selected galaxies associated with five DLAs with [M/H] > −0.3 all have high molecular gas masses, ≳5 × 1010 M ⊙. This indicates that the highest-metallicity DLAs at z ≈ 2 are associated with the most massive galaxies. The newly identified z ≈ 2.4604 Hi–selected galaxy, DLA0201+365g, has an impact parameter of ≈7 kpc to the QSO sightline, and an implied molecular gas mass of (5.04 ± 0.78) × 1010 × (α CO/4.36) × (r 31/0.55) M ⊙. Archival Hubble Space Telescope Wide Field and Planetary Camera 2 imaging covering the rest-frame near-ultraviolet (NUV) and far-ultraviolet (FUV) emission from this galaxy yield nondetections of rest-frame NUV and FUV emission, and a 5σ upper limit of 2.3 M ⊙ yr−1 on the unobscured star formation rate (SFR). The low NUV-based SFR estimate, despite the very high molecular gas mass, indicates that DLA0201+365g either is a very dusty galaxy, or has a molecular gas depletion time that is around 2 orders of magnitude larger than that of star-forming galaxies at similar redshifts.

Jansky Very Large Array Detections of CO(1–0) Emission in H i-absorption-selected Galaxies at z ≳ 2

We report a Karl G. Jansky Very Large Array search for redshifted CO(1–0) emission from three H i-absorption-selected galaxies at z ≈ 2, identified earlier in their CO(3–2) or CO(4–3) emission. We detect CO(1–0) emission from DLA B1228-113 at z ≈ 2.1933 and DLA J0918+1636 at z ≈ 2.5848; these are the first detections of CO(1–0) emission in high-z H i-selected galaxies. We obtain high molecular gas masses, M mol ≈ 1011 × (α CO/4.36) M ⊙, for the two objects with CO(1–0) detections, which are a factor of ≈1.5–2 lower than earlier estimates. We determine the excitation of the mid-J CO rotational levels relative to the J = 1 level, r J1, in H i-selected galaxies for the first time, obtaining r 31 = 1.00 ± 0.20 and r 41 = 1.03 ± 0.23 for DLA J0918+1636, and r 31 = 0.86 ± 0.21 for DLA B1228-113. These values are consistent with thermal excitation of the J = 3 and J = 4 levels. The excitation of the J = 3 level in the H i-selected galaxies is similar to that seen in massive main-sequence and submillimeter galaxies at z≳2, but higher than that in main-sequence galaxies at z ≈ 1.5; the higher excitation of the galaxies at z ≳ 2 is likely to be due to their higher star formation rate (SFR) surface density. We use Hubble Space Telescope Wide Field Camera 3 imaging to detect the rest-frame near-ultraviolet (NUV) emission of DLA B1228-113, obtaining an NUV SFR of 4.44 ± 0.47 M ⊙ yr−1, significantly lower than that obtained from the total infrared luminosity, indicating significant dust extinction in the z ≈ 2.1933 galaxy.

Silicon Photomultipliers Coupled to Scintillators With the Emission Maximum at 550 nm

A majority of the silicon photomultipliers (SiPMs) are sensitive to blue and near-ultraviolet (NUV) photons that are not optimized for scintillators with the emission maximum at wavelengths longer than 500 nm. The red–green–blue (RGB) SiPM is developed for the maximum photon detection efficiency (PDE) at 550 nm, which is a good match for some high-light-yield scintillators, such as CsI:Tl (CsI) and Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.5</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> :Ce (GYGAG). Comparisons are made for the performance of these scintillators coupled to the RGB SiPM and a blue-sensitive SiPM. Because it takes tens of nanoseconds for the microcells to recharge after registering a photon hit, the linearity of these scintillation detectors was studied for high-energy gammas where numerous scintillation photons are generated. In addition, the energy resolution of the 662-keV gamma emitted by <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs was measured for temperatures between −20 °C and 50 °C. The nonlinearity was observed above 1 MeV for all measurements, and however, it can be corrected by energy calibration using a third-degree polynomial. For CsI, the energy resolution is better with the blue-sensitive SiPM because of the lower dark count rate (DCR). In contrast, GYGAG coupled to the RGB SiPM has a better energy resolution for temperatures below 30 °C because of the well-matched emission spectrum and PDE distribution. Nevertheless, the advantage disappears for temperatures above 30 °C due to the higher DCR. It would be useful to further develop the RGB SiPM with a lower DCR and higher operating temperatures.

Content and temperature quenching of Tb3+-activated Bi3TeBO9 green phosphor excited by NUV/VIS light

At present, to extend the optical applications of telluro-borate materials, exploring the photoluminescence quenching behavior of telluro-borate phosphor activated with rare-earth ions has become a critical issue. In this report, we have investigated the content and temperature quenching of a novel Bi3TeBO9 (BTBO)-based phosphor doped with trivalent terbium (Tb3+) activators, which was prepared via a solid-state reaction. The occupancy site and oxidation state of dopant terbium were verified. Under near-ultraviolet (NUV)/visible (VIS) excitation, the title phosphor exhibits green emission with the dominant 5D4→7F5 transition of Tb3+. The visible green light is closely influenced by both the Tb3+ content and operating temperature. When the dopant Tb3+ content exceeds 11 ​mol%, the quenching occurs, resulting from the dipole–dipole interaction. Furthermore, the investigations on temperature quenching and chromaticity shifting show that the BTBO:Tb3+ phosphor is a promising green fluorescent material.

Hot white dwarf candidates from the IGAPS-GALEX cross-match

ABSTRACT White dwarf (WD) stars are often associated with the central stars of planetary nebulae (CSPNe) on their way to the cooling track. A large number of WD star candidates have been identified; thanks to optical large-scale surveys such as Gaia DR2 and EDR3. However, hot-WD/CSPNe stars are quite elusive in optical bands due to their high temperatures and low-optical luminosities. The Galaxy Evolution Explorer (GALEX) matched with the INT Galactic Plane Survey (IGAPS) allowed us to identify hot-WD candidates by combining the GALEX far-UV (FUV)and near-UV (NUV)with optical photometric bands (g, r, i, and Hα). After accounting for source confusion and filtering bad photometric data, a total of 236 485 sources were found in the GALEX and IGAPS footprint (GaPHAS). A preliminary selection of hot stellar sources was made using the GALEX colour cut on FUV−NUV&amp;gt; −0.53, yielding 74 hot-WD candidates. We analysed their spectral energy distribution (SED) by developing a fitting program for single- and two-body SED using an MCMC algorithm; 41 are probably binary systems (a binary fraction of ∼55 per cent was estimated). Additionally, we classified the WD star candidates using different infrared (IR) colours available for our sample, obtaining similar results as in the SED analysis for the single and binary systems. This supports the strength of the fitting method and the advantages of the combination of GALEX UV with optical photometry. Ground-based time-series photometry and spectra are required in order to confirm the nature of the WD star candidates.

Modelling simple stellar populations in the near-ultraviolet to near-infrared with the X-shooter Spectral Library (XSL)

We present simple stellar population models based on the empirical X-shooter Spectral Library (XSL) from near-ultraviolet (NUV) to near-infrared (NIR) wavelengths. The unmatched characteristics of the relatively high resolution and extended wavelength coverage (350–2480 nm, R ∼ 10 000) of the XSL population models bring us closer to bridging optical and NIR studies of intermediate-age and old stellar populations. It is now common to find good agreement between observed and predicted NUV and optical properties of stellar clusters due to our good understanding of the main-sequence and early giant phases of stars. However, NIR spectra of intermediate-age and old stellar populations are sensitive to cool K and M giants. The asymptotic giant branch, especially the thermally pulsing asymptotic giant branch, shapes the NIR spectra of 0.5–2 Gyr old stellar populations; the tip of the red giant branch defines the NIR spectra of older populations. We therefore construct sequences of the average spectra of static giants, variable O-rich giants, and C-rich giants to be included in the models separately. The models span the metallicity range −2.2 &lt; [Fe/H] &lt; +0.2 and ages above 50 Myr, a broader range in the NIR than in other models based on empirical spectral libraries. We focus on the behaviour of colours and absorption-line indices as a function of age and metallicity. Our models can reproduce the integrated optical colours of the Coma cluster galaxies at the same level as other semi-empirical models found in the literature. In the NIR, there are notable differences between the colours of the models and Coma cluster galaxies. Furthermore, the XSL models expand the range of predicted values of NIR indices compared to other models based on empirical libraries. Our models make it possible to perform in-depth studies of colours and spectral features consistently throughout the optical and the NIR range to clarify the role of evolved cool stars in stellar populations.

The GALEX-PTF Experiment. II. Supernova Progenitor Radius and Energetics via Shock-cooling Modeling

The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early ultraviolet (UV) observations of core-collapse supernovae (CC SNe). We present the results from a simultaneous Galaxy Evolution Explorer (GALEX) and Palomar Transient Factory (PTF) search for early UV emission from SNe. We analyze five CC SNe for which we obtained near-UV (NUV) measurements before the first ground-based R-band detection. We introduce SOPRANOS, a new maximum likelihood fitting tool for models with variable temporal validity windows, and use it to fit the Sapir & Waxman shock-cooling model to the data. We report four Type II SNe with progenitor radii in the range of R * ≈ 600–1100 R ⊙ and a shock velocity parameter in the range of v s* ≈ 2700–6000 km s−1 (E/M ≈ 2–8 × 1050 erg/M ⊙) and one Type IIb SN with R * ≈ 210 R ⊙ and v s* ≈ 11,000 km s−1 (E/M ≈ 1.8 × 1051 erg/M ⊙). Our pilot GALEX/PTF project thus suggests that a dedicated, systematic SN survey in the NUV band, such as the wide-field UV explorer ULTRASAT mission, is a compelling method to study the properties of SN progenitors and SN energetics.

Highly efficient hybridized local and Charge-transfer (HLCT) Deep-blue electroluminescence with excellent molecular horizontal orientation

Efficient deep-blue emitters with nice color purity are fundamental in organic light-emitting diode (OLED) applications. Herein, we report two phenanthroimidazole (PPI) derivative deep-blue emitters (DP, SP) with hybrid local and charge-transfer (HLCT) properties of high photoluminescence quantum yield (PLQY) and nice color purity. More importantly, the horizontal dipole orientation (Θ//) of them are both superior to the isotropic emitters (66.7%), especially the Θ// of SP is 89.5%, which can greatly improve its OLED performance. As a result, non-doped OLED of SP exhibits deep-blue emission with Commission Internationale de lEclairage (CIE) coordinate of (0.158, 0.068) and maximum external quantum efficiency (EQEmax) of 11.3%, which is nearly twice that of DP and is one of the best results among the non-delayed, non-doped deep-blue fluorescent OLEDs. Furthermore, SP-based doped OLED displays an excellent performance of near ultraviolet (NUV) emission at 406 nm with CIE coordinate of (0.157, 0.046) and EQEmax of 7.5%, which is also a competitive result in the materials with comparable NUV OLED applications.

Accretion and outflows in young stars with CUBES

The science case on studies of accretion and outflows in low-mass (<1.5M_{odot }) young stellar objects (YSOs) with the new CUBES instrument is presented. We show the need for a high-sensitivity, near-ultraviolet (NUV) spectrograph like CUBES, with a resolving power at least four times that of X-Shooter and combined with UVES via a fibrelink for simultaneous observations. Simulations with the CUBES exposure time calculator and the end-to-end software show that a significant gain in signal-to-noise can be achieved compared to current instruments, for both the spectral continuum and emission lines, including for relatively embedded YSOs. Our simulations also show that the low-resolution mode of CUBES will be able to observe much fainter YSOs (V sim22 mag) in the NUV than we can today, allowing us extend studies to YSOs with background-limited magnitudes. The performance of CUBES in terms of sensitivity in the NUV will provide important new insights into the evolution of circumstellar disks, by studying the accretion, jets/winds and photo-evaporation processes, down to the low-mass brown dwarf regime. CUBES will also open-up new science as it will be able to observe targets that are several magnitudes fainter than those reachable with current instruments, facilitating studies of YSOs at distances of sim kpc scale. This means a step-change in the field of low-mass star formation, as it will be possible to expand the science case from relatively local star-forming regions to a large swathe of distances within the Milky Way.

A Low-Noise CMOS SPAD Pixel With 12.1 Ps SPTR and 3 Ns Dead Time

Single-photon avalanche diodes (SPADs) have become the sensor of choice in many applications whenever high sensitivity, low noise, and sharp timing performance are required, simultaneously. Recently, SPADs designed in CMOS technology, have yielded moderately good performance in these parameters, but never equaling their counterparts fabricated in highly customized, non-standard technologies. The arguments in favor of CMOS-compatible SPADs were miniaturization, cost and scalability. In this paper, we present the first CMOS SPAD with performance comparable or better than that of the best custom SPADs, to date. The SPAD-based design, fully integrated in 180 nm CMOS technology, achieves a peak photon detection probability (PDP) of 55&#x0025; at 480 nm with a very broad spectrum spanning from near ultraviolet (NUV) to near infrared (NIR) and a normalized dark count rate (DCR) of 0.2 cps/<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m<inline-formula><tex-math notation="LaTeX">$^2$</tex-math></inline-formula>, both at 6 V of excess bias. Thanks to a dedicated CMOS pixel circuit front-end, an afterpulsing probability of about 0.1&#x0025; at a dead time of <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>3 ns were achieved. We designed three SPADs with a diameter of 25, 50, and 100 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m to study the impact of size on the timing jitter and to create a scaling law for SPADs. For these SPADs, a single-photon time resolution (SPTR) of 12.1 ps, 16 ps, and 27 ps (FWHM) was achieved at 6 V of excess bias, respectively. The SPADs operate in a wide range of temperatures, from &#x2212;65 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C to 40 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C, reaching a normalized DCR of 1.6 mcps/<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m<inline-formula><tex-math notation="LaTeX">$^2$</tex-math></inline-formula> at 6 V of excess bias for the 25 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m at &#x2212;65 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C. The proposed SPADs are ideal for a wide range of applications, including (quantum) LiDAR, super-resolution microscopy, quantum random number generators, quantum key distribution, fluorescence lifetime imaging, time-resolved Raman spectroscopy, to name a few. All these applications can take advantage of the vastly improved performance of our detectors, while enjoying the opportunities of megapixel resolutions promised by the economy of scale that is offered by CMOS technologies.

New Time-resolved, Multi-band Flares in the GJ 65 System with gPhoton

Abstract Characterizing the distribution of flare properties and occurrence rates is important for understanding habitability of M-dwarf exoplanets. The Galaxy Evolution Explorer (GALEX) space telescope observed the GJ 65 system, composed of the active, flaring M stars BL Cet and UV Cet, for 15,900 s (∼4.4 hr) in two ultraviolet (UV) bands. The contrast in flux between flares and the photospheres of cool stars is maximized at UV wavelengths, and GJ 65 is the brightest and nearest flaring M-dwarf system with significant GALEX coverage. It therefore represents the best opportunity to measure low-energy flares with GALEX. We construct high-cadence lightcurves from calibrated photon events and find 13 new flare events with near-UV (NUV) energies ranging from 1028.5–1029.5 erg and recover one previously reported flare with an energy of 1031 erg. The newly reported flares are among the smallest M-dwarf flares observed in the UV with sufficient time resolution to discern lightcurve morphology. The estimated flare frequency at these low energies is consistent with extrapolation from the distributions of higher-energy flares on active M dwarfs measured by other surveys. The largest flare in our sample is bright enough to exceed the local nonlinearity threshold of the GALEX detectors, which precludes color analysis. However, we detect quasi-periodic pulsations during this flare in both the far-UV and NUV bands at a period of ∼50 s, which we interpret as a modulation of the flare’s chromospheric thermal emission through periodic triggering of reconnection by external MHD oscillations in the corona.

A 6.4-yr optical quasi-periodic oscillations in SDSS J075217.84+193542.2: a new candidate for central binary black hole system

ABSTRACT In this manuscript, a 6.4-yr optical quasi-periodic oscillations (QPOs) is detected in the quasar SDSS J075217.84+193542.2 (=+SDSS J0752) at a redshift 0.117, of which 13.6-yr-long light curve from Catalina Sky Survey and All-Sky Automated Survey for Supernovae is directly described by a sinusoidal function with a periodicity 6.4 yr. The 6.4-yr QPOs can be further confirmed through the generalized Lomb–Scargle periodogram with confidence level higher than 99.99 per cent, and through the autocorrelation analysis results, and through the weighted wavelet z-transformation technique. The optical QPOs strongly indicate a central binary black hole (BBH) system in SDSS J0752. The determined two broad Gaussian components in the broad H α can lead to the BBH system with expected space separation about 0.02 pc between the expected two central BHs with determined virial BH masses about 8.8 × 107 and 1.04 × 109 M⊙. Meanwhile, we check the disc precessions applied to explain the optical QPOs. However, under the disc precession assumption, the determined optical emission regions from central BH have sizes about 40RG two times smaller than sizes of the expected Near UltraViolet (NUV) emission regions through the correlation between disc size and BH mass, indicating the disc precessions are not preferred. And due to the lower radio loudness around 0.28, jet precessions can be also totally ruled out. Furthermore, only 0.08 per cent probability can determined as the QPOs misdetected through light curves randomly created by the continuous autoregressive process, reconfirming the reported optical QPOs.